There are numerous circumstances in which a structure experiences time varied and location varied state changes. Such state changes may be heavily influenced by the environment in which the structure is placed or is operating. For example, there are numerous structures that experience a change in temperature, with the temperature varying from one location of the structure to another (i.e., temperature gradients and localized heating or cooling of the structure), and wherein the structure experiences changes in temperature at different times. In other words, such a temperature or other condition is often transient and asymmetric in multiple dimensions.
Often, it is desirable to manage the temperature (or other parameter or condition) of such structures. However, efforts to control such parameters in a structure have conventionally included “blanket” approaches that are generally conservatively designed, often for worst-case scenarios.
For example, one structure that is desirably maintained within a certain temperature range includes the leading edge of a wing foil on supersonic or hypersonic aerospace vehicle. Similarly, the wall (or some other component) of an engine that is associated with high-speed aerospace vehicles experiences substantial temperature variations and may require some form of thermal management for effective operation of the vehicle. Depending, for example, on the current speed of the vehicle, the acceleration pattern of the vehicle and numerous other parameters, such surfaces and structures may experience very substantial temperature increases, with such increases sometimes occurring at a rather rapid pace and in a non-uniform manner.
Conventional cooling approaches for structures associated with, for example, high-speed aerospace vehicles, can be broadly classified as film cooling, where the wall is covered with a thin film of fresh coolant (often fuel), transpiration cooling, where the coolant is supplied uniformly through a porous wall, and wall cooling, where coolant flow convectively cools the back side of the wall. Conventionally, these approaches are implemented passively wherein one or more arrays of fixed orifices are supplied with a pressurized coolant without substantial control over the volume of coolant or the location to which such coolant is supplied. Such approaches can often present a number of challenges and problems.
During the trajectory of a typical hypersonic air-breathing vehicle (e.g., Mach 2-15), the heat transfer thermal loads can vary dramatically, from take-off to the mission altitude, as illustrated in FIG. 1. FIG. 1, which illustrates the large temporal variations of heat load on the external skin of a hypersonic vehicle for a typical mission, shows that the maximum convective heat transfer coefficient, “h” and the adiabatic wall temperature, Taw occur at different times in the trajectory of such a vehicle (note that the speed of such a vehicle after 95 seconds is approximately Mach 3). Such large variations in thermal loads impose tremendous demands on a vehicle thermal management system, typically requiring the cooling system to be designed for a fixed worst-case trajectory point. Though this design approach may provide adequate cooling at the highest thermal loads point, it comes at the expense of potentially over-cooling at other “off-design” points. This approach is inefficient, requires an undesirably high volume of coolant and places stringent demands on the thermal management system for the entire mission.
Similar inefficiencies may result from the spatial distribution of thermal loads over the surface of the structure being cooled. Uncertainty in predicting the temperature at any particular location within a given structure (e.g., the inlet, combustor, or nozzle walls of an engine) will lead to conservative coolant flow rates for the entire structure.
Numerous other structures likewise function more effectively if maintained within a desired temperature range (or within other specified parameter limits) but suffer from similar inefficiencies in maintaining the desired parameters. For example, with respect to temperature or thermal management, other examples of structures, where it is desirable to maintain the structure within a specified temperature range includes gas turbine blades, nuclear reactors, combustors, heat exchangers, rocket engines and various components of aerospace vehicles including hypersonic vehicles. In actuality, the number of components and structures that require some kind of parameter (e.g., thermal) management, and wherein the parameter is transient and asymmetrical is virtually limitless.
It is an ongoing desire to improve management of other parameters that may be time or spatially varied (or both). It would be advantageous to improve the efficiency and effectiveness of such parameter management including the use of structures, systems and methods that are adaptive in nature. For example, it is an ongoing desire to improve thermal management of various structures that exhibit time varied or spatially varied temperature changes.